HDL, the major antiatherogenic lipoprotein, may play an important role in reverse cholesterol transport, a complex process modulated by the action of multiple enzymes, transfer proteins and receptors. LCAT, CETP and HL are essential for the esterification, exchange and hydrolysis of lipids present in HDL and modulate plasma HDL concentrations, heterogeneity and metabolism. Through their action on HDL, these 3 proteins may also play a major role in the development of atherosclerosis. In order to investigate the LCAT, CETP and HL gene-gene interaction in vivo we have utilized recombinant adenovirus to express human HL and CETP in transgenic mice overexpressing human LCAT at plasma levels 100 fold higher than control mice. Compared to control animals, LCAT transgenic mice have increased plasma TC, CE and HDL-C concentrations as well as marked HDL heterogeneity. Unlike humans, mice are deficient in CETP activity and thus, in these animals CETP-mediated lipid exchange between HDL and apoB containing lipoproteins does not occur. Adenovirus-mediated expression of HL in control and LCAT transgenic mice resulted in post-heparin plasma HL activity of 24482+7440 and 27549+9755 nmol/m/ml, respectively and approximately 50-60% reduction in plasma TC, PL and HDL in both groups. Compared to control animals, HL expression in transgenic mice resulted in preferential hydrolysis of the apoE-rich HDL as well as normalization of the heterogeneous HDL profile thus establishing a coordinate role for these two enzymes in modulating HDL particle heterogeneity. Adenovirus-mediated expression of CETP in control and LCAT transgenic mice resulted in plasma CETP activity of 80+4 and 74+5 %/5 ul/l8h, respectively and increased plasma apoB lipoproteins as well as decreased HDL concentrations, a lipoprotein pattern reminiscent of human profiles which indicates effective CETP-mediated transfer of CE from HDL. Compared to control animals, expression of CETP in LCAT transgenic mice resulted in a more protective lipoprotein profile, thus establishing the coordinate role of CETP and LCAT in HDL metabolism.